Electrodeposition of manganese and cathode therefor



. I P7tented Aug. 3, 1943 ELECTRODEPOSITION OF MANGANESE AND CATHODETHEREFOR Harold L. Chamberlain, Knoxville, Tenn., assignor to ElectraManganese Corporation; Minneapolis, Minn., a corporation of Delaware NoDrawing. Application January 2, 1941,

' Serial No. 372,827

Claims.

This invention relates to a cathode for use in the electrowinning ofmanganese and other pufposes and to a process of using said cathode.

Some of the requirements which must be met by a successful cathode forthe electrodeposition of manganese; particularly in the electrowinningof manganese from solution prepared from manganese containin ore will bestated as follows:

1. It is necessary to use some substance other than manganese as thismetal is too brittle to be used as such.

2. That substance must be one from which the deposited manganese can bereadily separated,

e. g., by flexing, bending, hammering, etc., preferably by flexing.Therefore the cathode must be strong, tough, and resilient and notreadily subject to permanent deformation.

3. The cathode must be of such a nature that the manganese will adherethereto during electro deposition but will readil part or separatetherefrom, completely, after the deposition is completed, by any of themechanical operations above mentioned. If portions of the manganeseadhere to the cathode so firmly as to require laborius mechanicaloperations for their removal or any extensive chemical treatment, thecathode is unsatisfactory for successful commercial operation.

4. The cathode must be so inert that it will not be affected by cleaningcompounds so as to form a rust" or deposit which would contaminate theelectrolyte or interfere with the manganese deposit. I

5. The cathode must be so inert that if any manganese adheres thereto asa residue after the removal of the cathodic deposit as a whole, saidresidue may be readily removed by a simple chemical treatment withoutcorroding or otherwise impairing the surface, so that a simple buffingoperation will restore the surface to a com fore the cathode must be soinert that it will not cause any contamination of the electrolyte ordirect contamination of the manganese deposit. More specifically, thecathode must be sufficiently inert so that substantially no corrosion iscaused by galvanic or other action at the solution line.

9. The elfectivelife of the cathode, i. e., the time during which itwill meet the above requirements, must be at least 5,000 hours.

These requirements and the difficulty of meeting them have created aproblem. Numerous unsuccessful efiorts have been made, prior to thisinvention, to solve that problem.

It is an object of this invention to solve that problem and to therebyprovide a successful cathode adapted for the deposition of manganese,

particularly in the other metals.

It is a further object to provide a' process of making said cathode, toimprove its desirable characteristics and performance.

It is a further object to provide a process of electrowinning thereof,and

using said cathode for the deposition ofmanganese andother metals.

An understanding of the invention will be assisted by a brief resume ofsome of the unsuccessful efforts to solve the problem which forms thebackground of the invention.

In the electrowinning of manganese, the cell is divided into twocompartments, 9. catholyte chamber and an anolyte chamber, separated bya permeable membrane. Both chambers contain a suitable manganese saltusually manganese sullr phate and usually ammonium sulfate. Owing ditionwhich permits of another plating cycle and subsequent easy removal ofthe manganese.

6. The surface of the cathode should be capable of receiving a highpolish.

7. The cathode must be sufliciently resilient to permit flexingwithoutpermanent deformation, and sufficiently free from stresses sothat it does not warp.

8. One of the fundamental purposes of obtaining metallic manganese bythe electrowinning process, as distinguished from other methods, is toobtain the manganese in a state of high purity and to this end. theelectrolytes are prepared in a condition of high purity in respect ofmetals that would cause contamination. Thereposit by flexing,bending-and hammering. Not

to electrolysis, the pH of the catholyte may be about 6.5 to 8.0 andthat of the anolyte 0.5 to 1.5.

The concentration of manganese, as sulphate may be 25 to 35 grams perliter in the catholyte chamber and from 15 to 25 grams per liter in theanolyte chamber. about to grams per liter of ammonium sulphate.

The unsuccessful efforts reviewed below were made under comparableconditions in catholytes within the above concentrations. The cathode ineach case was a metallic sheet measuring about 18' by 36 inches immersedin the catholyte to a depth of about 30 inches.

First, cold rolled steel was used during a period of 48 hours. Thecathode was then removed and an attempt made to remove the manganesedeonly was it almost impossible to remove the deposit but, on analysis,the deposit when finally removed was found to contain 0.1 percent ofiron Each chamber may contain which was much beyond the saleable limitfor electrolytic manganese. After various treatments including buffing,rindin oilin and p vating" (treatment with dilute bichromate solution)of the steel surface, it was possible to get a surface from which themanganese could be more readily removed, but this treatment did notovercome corrosion and contamination of the catholyte. Corrosionproducts formed on the suriace oi the cathode exposed to air, droppedinto the catholyte and introduced iron salts which contaminated theelectrolyte and the deposit. Etching of the cathode at the electrolyteair junction also occurred and caused contamination of the electrolyteand the manganese deposit.

Copper, lead, tin and tin plate were tried. All

of these caused serious contamination of the electrolyte andof themanganese deposit and the tin coating peeled off with the manganesedeposit, Serious contamination was also caused by Monel metal, purenickel and "id-8 alloy (18% chromium, 8% nickel and the balance iron).The iron alloy containing 17 percent chromium was satisfactoryrior about480 hours of cyclic use which was much too short to be economical. Atthe end of this period it was so badly etched that the manganese couldnot be satisiactoriiy removed therefrom on further use.

The noble metals were too expensive either as such or in the form ofcoatings. Cold rolled tantalum was also too expensive and not sumcientlyinert.

Iron alloys containing 18 percent chromium and 12 percent nickel and thebalance iron and those containing 24 percent chromium and 18 percentnickel and the balance iron were also found to be unsatisfactory.

It was finally discovered that austenitic alloys illustrated by-thecomposition 18 percent chromium, 12 percent nickel, 2 to 4 percentmolybdenum and the balance iron provided means for a solution'of theproblem.

In accordance with this invention, an alloy having a composition withinthe limits chromium 1'1 to 19 percent, nickel 11 to 13 percentmolybdenum 2 to 4 percent and the balance iron is first annealed toremove stresses and eliminate warping. It is then surface hardened bycold Working, e. g., by grinding the surface with 80 mesh grit. Thisimparts resilience. The sheet can then be cold rolled withoutsubstantially altering the dimensions and is cold rolled in order toproduce a planar surface, smooth out grinding marks and furtherwork-harden the sheet. After this is done, the sheet is polished andthen possesses a combination of properties meeting the above listedcriteria. The hardening operations, e, g., surface grinding and coldrolling, are continued until the desired degree of resilience isimparted, i. e., until the sheet is sufficiently resilient and elasticto be capable of temporary deformation to remove the metallic depositsuch as flexing, for example, without permanent deformation.

The process of using the cathode of the present 1 invention may beillustrated as follows; this process being a cycle which is continuouslyrepeated.

The cathode is placed in the cathode-chamber and manganese is depositedthereon. ,The cathode and its adhering manganese deposit is thenremoved, washed to remove electrolyte and dried as for example in acurrent of hot air, the washing step being preferably preceded bytreatment with a dilute bichromate solution to passivate the deposit andprevent oxidation during drying. The cathode and manganese deposit isthen maasaaeco nipulated to remove the manganese as for example bybending or flexing over a curved surface. If any-residual manganesescrap remains on the cathode, it is removed by treatment with dilutemineral acid, e. g., 3 per cent sulphuric acid or othersuitable solventand then washed with water to remove the solvent. Instead of treatmentwith an acid or other solvent, said residual manganese may be removedelectrolytically. This may be done by employing the cathode withresidual adherent manganese as an anode in an alkaline electrolyte, e.g., 5 per cent K2003 and lead as a. cathode or in an acid electrolyte,for example, anolyte such as employed in manganese electrowinning. Dirtand grease are then removed, as for example by treatment with a suitableemulsifying agent, e. g., soap, soda ash, trisodium phosphate,sulfonates, salts of sulfated alcohols, etc, and other detergents or byknown methods of electrolytic cleaning. It is then bufied andpolished'as for example by the application of high speed cotton buihngwheels and a buffing compound containing wax or the like and a chromiumoxide powder known in the trade as green rouge. It is then treated withan organic solvent to remove the buffing compound and is ready 7 foranother cycle of use in the electrolytic cell.

' I claim:

1. A cathode adapted for the electrolytic deposition of a brittle metalthereon and the ready removal of said deposit therefrom, said cathodebeing in sheet form, having a substantially planar surface, sufiicientlyfree from stresses to prevent warping, suficiently resilient to permitflexing without permanent deformation, sufficiently inert to preventsubstantial contamination of the electrolyte and manganese deposit, saidcathode being an annealed, surface ground, cold rolled and surfacepolished alloy 7 having the composition; chromium 17 to 19 per cent,nickel 11 to 13 per cent, molybdenum 2 to 4 per cent and the balanceiron.

2. A cathode adapted for the electrolytic deposition of a metal thereonand the ready removal of said deposit therefrom, said cathode being insheet form, having a substantially planar surface, sufficiently freefrom stresses to prevent warping, sufliciently resilient to permitflexing without permanent deformation, sufficiently inert to preventsubstantial contamination of the electrolyte and manganese deposit,

said cathode being an annealed surface ground,

cold rolled and surface polished alloy having the composition; chromium18 per cent, nickel 12 per cent, molybdenum 2 to 4 per cent and thebalance iron. I

3. The process of making a cathode adapted for the electrolyticdeposition of a metal thereon and the ready removal of said deposittherefrom which comprises providing an alloy in sheet form having thecomposition; chromium 1'7 to 19 per cent, nickel 11 to 13 per cent,molybdenum 2 to 4 per cent, and the balance iron, annealing said sheet,hardening the surface thereof and cold rolling said sheet, until aresilience is imparted thereto sufficient to permit flexing for thepurpose of removing a brittle metallic deposit therefrom, and impartinga surface polish.

4. The process of electrolytically depositing manganese on a cathode,removing said deposit therefrom and conditioning the' cathode forasubsequent deposit which comprises electrolytically depositing a metalfrom an aqueous solution of a salt of said metal on a cathode in sheetform, said cathode being an annealed, surface hardened, cold rolled andsurface polished alloy in sheet form having' the composition; chromium1'7 to 19 per cent, nickel 11 to 13 per cent, molybdenum 2 to 4 percent, and the balance iron, removing the cathode and its attacheddeposit from the electrolyte, washing it with water and drying it,flexing the cathode'and removing the metallic deposit therefrom,removing traces of adhering metallic deposit from said cathode, washingthe cathode with water, removing dirt and 10 grease from the cathode,and imparting a polish to the surface of the cathode.

5. A process for the electrolytic deposition of manganese on a cathodeand removing it therefrom whichcomprises passing a direct currentbetween an anode and a cathode and through an electrolyte containing amanganese salt 'in solution therein, the cathode being in sheet form andhaving the composition; chromium about 17 to about 19 per cent, nickelabout 11 to about 13 per cent, molybdenum about 2 to about 4 per centand the balance iron, plating metallic manganese on said cathode andstripping from said cathode the manganese plated thereon.

HAROLD L. CHAMBIIEL'LKILAIIT.

